This invention relates to dispensing systems for liquids and for suspensions, such as paints, having liquid carriers. Such liquids and suspensions will hereafter be referred to collectively as liquids.
The paint manufacturer is faced with the perennial problem of supplying to its customers many different coloured paints and usually more colours than the manufacturer can as a practical matter keep in stock. The problem is especially acute in the supply of paint for vehicle refinishing, that is to say in the supply of paint for respraying vehicles, for example, a crash repair. The difficulty is that vehicle manufacturers supply their vehicles in many different colours and in subtly different shades. Even for a given make, model and colour slight variants can arise between the exact colours of particular cars because of variants in the batches of paint used in manufacture. Moreover, commercial transport operators often wish to respray their vehicles in their own distinctive liveries. As a result, the number of paint colours in use is extensive and may be as high as 30,000.
Paint manufacturers succeed in providing the large number of colours called for by a method of blending. A number of basic or standard colours are produced that usually contain a single pigment but may contain a major proportion of one pigment and a minor amount of another sufficient to produce the standard colour. A typical standard range will contain from 20 to 50 basic colours which can be blended to give thousands of other colours. Thus, the refinisher or refinish paint supplier is in the position that it needs to stock between 20 to 50 colours only depending upon the particular range of paints that it wishes to supply.
In order to match the cars the refinisher repairs, the refinisher must mix these paints very carefully and very accurately against a formula or mixing scheme which is supplied by the paint manufacturer. The mixing scheme will set out the proportions of basic colours which have to be mixed to match the exact colour of the particular make, model and colour variant of the repaired car.
It is important that the basic colours are supplied and maintained in a very consistent condition. It is also important that they be dispensed very accurately indeed, against a formulation which is accurate to start with.
In providing an ideal dispensing system for use in paint blending there are certain desirable objectives, namely
(1) accurate blending PA1 (2) efficient operation without maintenance problems. PA1 (3) automatic operation PA1 (4) low cost
In automatic dispensing systems there is usually a requirement to have some form of recirculation of the paint to prevent settling of the pigment.
There are several disadvantages in the systems on sale today, one of which is the large size of valves used and from which the paint is required to be dispensed into say either a 21/2 liter container or a 1 tonne container as selected. The consequence of having a number of bulky valves is that it is impossible to position all of them above a container of any practical size. Thus one has an immediate problem of directing the paint to be dispensed into the container. There are two obvious solutions. One is to move the container every time a dispense is required so that the centre of the container is positioned under the valve to be used for that particular dispense. This is obviously inconvenient and can be error prone. It is particularly inconvenient in the case of machines where the container may weigh one tonne or more. An alternative way is to move the valves to always position the valve which is about to dispense above the centre of the container. There are at least two known ways of doing this. In one method the machine has a huge crescent shaped carriage on which the valves are mounted and this carriage swings around in a great arc in order to position each of the valves above a container. Because the valves swing by such a large amount (several metres) the pipes leading to the valve have to be flexible. Not only that but since the length of pipe varies as the mounting plate swivels there has to be some other means of adjusting the length which in turn involves another compensating mechanism with flexible hoses. The degree of complexity that would be introduced if one had recirculation within these flexible pipes is so immense that the requirement of recirculation has to be omitted.